Adhesion of Multifunctional Substrates for Integrated Cure Monitoring Film Sensors to Carbon Fiber Reinforced Polymers

Abstract

During fiber composite production, the quality of the manufactured parts can be assured by measuring the progress of the curing reaction. Dielectric film sensors are particularly suitable for this measurement task, as they can quantify the degree of curing very specifically and locally. These sensors are usually manufactured on PI films, which can lead to delaminations after integration. Other authors report that this negative influence can be reduced by miniaturization and a suitable shaping of the sensors. This article pursues as an alternative, a novel approach to achieve a material closure instead of a geometrically generated form closure by choosing suitable thermoplastic materials. Thermoplastic films made of PEI, PES and PA6 are proposed as carrier substrates for thin film sensors. They are investigated with regard to their mechanical effects in FRP. The experiments show that the integration of PES and PEI in FRP has the best shear strength, but PA6 leads to a higher critical energy release rate during crack propagation in mode I. For PI, a locally strongly scattering critical energy release rate was observed. Neither in tensile nor in Compression After Impact (CAI) tests a significant influence of the films on these characteristic values could be proven.

Tensile Strength and Structure of the Interface between a Room-Curing Epoxy Resin and Thermoplastic Films for the Purpose of Sensor Integration

“…Such an interphase formation has already been reported in the literature for the thermoplastics PEI and PES [5,[18][19][20][21]. In our own preliminary tests on these thermoplastics embedded in prepreg specimens, no impairment of the interlaminar shear strength and a significant improvement of the critical energy release rate in Mode I was observed for these thermoplastics, with PEI being significantly better than PES [12].…”

“…Figure 1 highlights the mechanical impact of film sensors as an important issue for sensor integration and also shows different other questions arising from the integration of film sensors for cure monitoring purposes. The mechanical impact has already been observed in earlier experiments on critical energy release rates [12]. One way to reduce the weakening effect is to provide holes in the film through which the epoxy resin can crosslink [7,13,14].…”

“…The mechanical impact has already been observed in earlier experiments on critical energy release rates [12]. One way to reduce the weakening effect is to provide holes in the film through which the epoxy resin can crosslink [7,13,14]. Another approach is to produce films out of plasticized epoxy resin [15].…”

“…Previous investigations have already shown Figure 1. Questions arising from the integration of film sensors for cure monitoring purposes, modified from [12].…”

“…In the case of polyamide 6 (PA6) there is good compatibility between several molecular functional groups of the thermoplastic and the epoxy resin [17]. Previous investigations have already shown that integrated PA6 films have little effect on the interlaminar shear strength and can significantly increase the critical energy release rate in Mode I [12]. Compounds between polymers such as epoxy resins and thermoplastics can enable a special form of adhesion, namely a so-called interphase developed between both materials.…”